With Dennis booked in for season-ending knee surgery, Hoiles will play blindside flanker as the Waratahs look to clinch a precious home semi-final after victory over the Highlanders in Sydney on Sunday.

Hoiles' promotion comes four months after Cheika revived the 32-year-old's career after the one-time Wallaby made a desperate last-ditch trip to Sweden for radical surgery to repair a chronic achilles tendon injury.

Cheika had several options at his disposal, including moving Jacques Potgieter to the back row and starting Wallabies sensation Will Skelton at lock.

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He could also have drafted lineout ace Mitch Chapman into the second row and handed Potgieter Dennis's No.6 jumper.

But just hours after indicating otherwise, Cheika decided to bank on Hoiles, a former Brumbies captain with 114 Super Rugby caps to his name.

Cheika, though, did qualify his selection with the promise he'd likely shuffle the pack again for next weekend's final-round showdown with the Queensland Reds.

"The conservative thing to do is put Stephen straight in. He's done it before," Cheika said.

"But I think we've shown in the past that we're looking to be far from conservative and we're looking to be more progressive in what we do.

"My experience tells me at this end of the season that if you try to hang in there and stay at the same standard, you'll fail.

"You've got to keep progressing and keep moving forward, evolving your game to give the opposition different things to deal with."

Already guaranteed a playoff spot after locking up the Australian conference with a club-record-equalling five straight victories, the Waratahs still need to win one of their remaining two games to be sure of hosting a semi-final at Allianz Stadium.

Little wonder the famously guarded coach wasn't prepared on Tuesday to revise his long-stated goal of a top-two finish and start targeting the minor premiership.

The Waratahs are unbeaten at home this campaign, but Cheika insists the fourth-placed Highlanders are capable of crashing the party and leaving his side under pressure to topple the Reds in Brisbane to avoid a dreaded away final.

"They're equal top of the New Zealand conference," he said.

"On Sunday, it's probably the game I'm going to ask the team to make the biggest sacrifices of the season so far."